The present invention relates to optical recording methods and more particularly to a technique based on land/groove recording and suitable for performing high-density optical recording in which the track width is smaller than the optical spot diameter.
A conventional method is disclosed in, for example, JP-A-59-191156. In the prior art, a laser beam generated from a laser diode carried on an optical head is formed into a collimated beam by means of a collimating lens, and the collimated beam passing through a beam splitter is focused by an objective lens so as to be converged into an optical spot on a magneto-optical recording medium. The position of the optical spot on the magneto-optical recording medium is controlled by moving the lens or the optical head by means of an optical spot scanning control means. Reflected light from the magneto-optical recording medium is guided to a photodetector through a beam splitter. A readout signal from the photodetector is processed by a reproduction circuit so as to be converted into reproduced data. Control of overall reproduction is carried out by a controller.
JP-A-6-176404 describes a technique for performing high-density (narrow track) recording.
A recording medium disclosed in JP-A-6-176404 is illustrated, in plan view form, in FIG. 5. Grooves 501 and lands 502 are formed on a substrate, information recording areas are formed in association with both the groove and the land, and prepits 504 are disposed on an extension line 503 of the boundary line between a groove 501 and a land 502. Prepits 504 are positioned each groove on only one side relative to the center line of each groove. With this construction, recording information is recorded on both the groove 501 and the land 502, address information representative of the recording areas are recorded in the form of prepits 504, and one prepit is used in common to a pair of adjacent groove 501 and land 502 to provide address information therefor.
When the technique as above is applied to, for example, a phase change recording medium or a magneto-optical recording medium, interference of information (crosstalk) between adjacent grooves 501 or lands 502 due to the optical interference effect within an optical spot 505 can be prevented, thereby permitting narrowing of track. On the other hand, in the prepit area free from the optical interference effect, the address information can be common to the paired groove and land and the effective track pitch can be increased to reduce crosstalk.
In the example of JP-A-6-176404, however, the disposition of the prepit area is offset on one side of the center line of the groove and an offset tracking error signal is delivered out of the prepit area, with the result that when an optical spot is caused to track a groove or a land, a tracking error (tracking offset) increases, making it difficult to perform high-density recording in which the track pitch is narrowed.